Self-draining ullage fuel tank systems and related methods

ABSTRACT

Self-draining ullage fuel tank system and related methods are described. An example fuel tank apparatus includes a fuel tank and a ullage tank positioned at an elevation relative to the fuel tank. The example fuel tank apparatus also includes a fluid path to fluidly couple a cavity of the fuel tank and a cavity of the ullage tank. The fluid path having a first end coupled to the cavity of the fuel tank. The fluid path having a second end extending through an opening of an upper wall of the ullage tank and having an opening positioned adjacent a bottom surface of the cavity of the ullage tank.

FIELD OF THE DISCLOSURE

This patent relates generally to fuel tanks and, more specifically, toself-draining ullage fuel tank systems and related methods.

BACKGROUND

Government agency regulations (e.g., regulations provided by the UnitedStates Coast Guard, Department of Transportation) require boat and/ormarine craft fuel systems to employ evaporative emissions controls toreduce or minimize evaporative emissions (e.g., hydrocarbons). In someinstances, evaporative emissions may leak from the fuel system due to,in part, an excess amount of fuel in a fuel tank of the fuel system. Forexample, in some instances, fuel within the fuel tank may expand duringoperation and/or non-operation of the marine craft. Such expansion offuel may be caused by, for example, temperature variations, a refuelingevent, etc. To allow for expansion of the fuel, a fuel tank of a marinecraft typically includes a ullage space (e.g., a volume within acontainer or tank that is to remain empty or unfilled) to allow for theexpansion of fuel vapors and limit the amount of evaporative emissionsemitted during operation and/or non-operation of the boat and/or othermarine craft. However, the ullage space reduces the overall liquid fuelvolume capacity of the fuel tank. As a result, known marine fuel systemsoften require use of a separate overflow or ullage tank to increase avolume capacity of the fuel tank.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example fuel tank assembly having an exampleself-draining ullage fuel tank in accordance with the teachingsdisclosed herein.

FIG. 2 depicts a flowchart of an example method to assemble an exampleself-draining ullage fuel tank system disclosed herein.

DETAILED DESCRIPTION

To reduce or minimize evaporative emissions, marine fuel systemstypically employ a fuel tank system providing a ullage or vapor space(e.g., an unfilled space in a container) that allows for the expansionof liquid fuel (e.g., after a refueling event). For example, governmentregulations or a manufacturer recommendation may require a certainpercentage of a vapor dome or ullage space (e.g., a 5% ullage) whenfilling the fuel tank to allow for fuel expansion.

Some known marine crafts may employ a fuel tank that includes adedicated ullage space to allow for the expansion of the fuel. However,because the ullage space of the fuel tank reduces an overall volume orliquid fuel capacity, a separate chamber or ullage tank is oftenemployed to increase or provide additional fuel volume capacity. Theseparate ullage tank enables liquid fuel in a fuel tank to flow into theullage tank when the fuel expands due to, for example, an increase inpressure in the fuel tank. As a result, the ullage tank increases theoverall volume or liquid fuel capacity of a fuel system. To enable thereturn of the fuel from the ullage tank to the fuel tank without the useof an external mechanical device (e.g., a pump), the ullage tank isoften positioned at an elevation relative to (e.g., a position above)the fuel tank. As a result, the liquid fuel in the ullage tank is ableto return freely into the fuel tank after a liquid fuel expansion event(e.g., when an engine of a fuel system demands fuel). Additionally, toallow the liquid fuel in the ullage tank to flow freely into the fueltank, the fuel tank is typically coupled to the ullage tank via acoupling positioned in a bottom wall or surface (to provide a fluid paththerethrough) of the ullage tank to enable substantially all of the fuelin the ullage tank to return or drain to the fuel tank via, for example,gravity. As a result, the ullage tank is self-draining because it allowssubstantially all of the liquid fuel to empty into the fuel tank withoutthe use of a mechanical device (e.g., a pump).

Although the above-mentioned couplings may employ a gasket and/or a sealto prevent evaporative emissions, the seal may fail, erode and/or becomedislodged, thereby causing liquid fuel and/or fuel vapors in the ullagetank to leak to, for example, the environment. While in some instancesthe ullage tank may be classified (e.g., by government agencies) as avent, in other instances a ullage tank may be classified as a fuel tankand, thus, must meet certain governmental regulations. For example,government agencies (e.g., the United States Coast Guard, Department ofTransportation) have enacted regulations that require each fittingcoupled to a fuel tank to be located at a top wall of the fuel tank toprevent leakage of liquid fuel should the seal or gasket fail.Therefore, ullage tanks that are classified as a fuel tank instead of avent may require fittings to be positioned at a top wall or surface ofthe ullage tank. As a result, such ullage tanks having fittingspositioned at a top wall or surface may require use of an externalmechanical device (e.g., a pump) to ensure that all of the liquid fuelis drained from the ullage tank and to the fuel tank when a component ofa fuel system (e.g., an engine) demands fuel.

Example ullage tank systems and related methods disclosed herein providea self-draining ullage tank having fittings positioned on an upper wallor surface of the ullage tank. In other words, the example ullage tanksystems and related methods disclosed herein eliminate having to providea coupling that provides a fluid path through a bottom or lower surfaceor wall of a ullage tank. Such a coupling is typically required orneeded to drain the ullage tank without use of an external mechanicaldevice (e.g., a pump). As a result, the example ullage tank systems andrelated methods disclosed herein comply with certain United Statesfederal agency regulations requiring all fittings of a fuel tank to bepositioned at an upper wall or surface of the fuel tank. Additionally oralternatively, the example ullage tank systems and related methodsdisclosed herein enable liquid fuel in an example ullage tank tosubstantially drain and/or return to a fuel tank without the use of anexternal mechanical device (e.g., a pump).

As used herein, a “fluid” includes, but is not limited to, a liquid suchas fuel (e.g., gasoline), a vapor such as fuel vapor (e.g., gasolinevapor), a gas (e.g., air) and/or any combination or mixture thereof.

FIG. 1 illustrates a portion of an example fuel system 100 of a boatand/or marine craft 102 disclosed herein. The example fuel system 100has an example fuel tank assembly 103 employing an example self-drainingullage tank 104 in accordance with the teachings disclosed herein.Referring to the example of FIG. 1, the example fuel tank assembly 103includes the ullage tank 104 fluidly coupled to a fuel tank 106. Thefuel tank 106 receives and/or supplies fuel to an engine 107 via a fuelline 108. The ullage tank 104 is fluidly coupled to a vapor collectionapparatus 110 (e.g., a carbon canister), which is coupled to a vent 112.

As shown in the illustrated example, the ullage tank 104 is elevated(e.g., spaced apart by a vertical distance) relative to the fuel tank106. For example, a bottom portion, wall, or surface 114 of the ullagetank 104 is positioned at a distance, elevation or height 116 (e.g., avertical or lateral height) relative to an upper portion, surface, orwall 118 of the fuel tank 106. As described in greater detail below,separating the ullage tank 104 and the fuel tank 106 by the height 116provides, for example, a pressure head when the ullage tank 104 is atleast partially filled with liquid fuel. As a result, the height 116 ofthe ullage tank 104 relative to the fuel tank 106 enables the ullagetank 104 to self-drain into the fuel tank 106 via, for example, a siphoneffect.

The ullage tank 104 of the illustrated example includes one or morewalls 120 to define a cavity 122. Likewise, the fuel tank 106 includesone or more walls 124 to define a cavity 126. As shown in the example ofFIG. 1, a fluid path 128 fluidly couples the cavity 122 of the ullagetank 104 and the cavity 126 of the fuel tank 106. The fluid path 128 ofthe illustrated example may be, for example, a conduit (e.g., stainlesssteel piping), tubing (e.g., fuel resistant tubing such as polypropyleneand/or other plastic material), etc. The fluid path 128 of theillustrated example includes a first end 130 coupled to the fuel tank106 and a second end 132 coupled to the ullage tank 104. In particular,the first end 130 of the fluid path 128 of the illustrated example iscoupled to the upper wall 118 of the fuel tank 106 via, for example, afitting 133, plastic welding, etc. Although not shown, in some examples,the first end 130 of the fluid path 128 is configured to extend into thecavity 126 of the fuel tank 106 a predetermined distance associated witha maximum, target and/or other desired liquid fuel level within the fueltank 106.

The second end 132 of the fluid path 128 of the illustrated example iscoupled to the ullage tank 104 through an opening 134 formed in an upperwall 136 (e.g., opposite the bottom wall 114) of the ullage tank 104. Afitting 138, for example, may be coupled to the opening 134 to supportat least a portion of the fluid path 128 extending through the opening134. Further, the second end 132 of the fluid path 128 of theillustrated example extends into the cavity 122 of the ullage tank 104such that an opening 140 of the second end 132 is substantially adjacentor spaced away (e.g., a quarter inch, a half-inch, an inch, etc.) fromthe bottom surface 114 of the cavity 112 of the ullage tank 104. In theillustrated example, a support, guide, fitting or other mount 142 may beprovided adjacent the bottom surface 114 of the ullage tank 104 tosupport the second end 132 of the fluid path 128 inside the cavity 122adjacent the bottom surface 114. As a result, the example ullage andfuel tanks 104 and 106 are fluidly coupled together without having toprovide a drain or a fitting through the bottom surface 114 of theullage tank 104. Further, as described in greater detail below, theliquid fuel from the cavity 122 of the ullage tank 104 is evacuated orremoved without the use of an external mechanical force or device (e.g.,a pump). Thus, by having the first end 130 of the fluid path 128 coupledto the upper wall 118 of the fuel tank 106 and the second end 132passing through the upper wall 136 (and not the bottom surface 114) ofthe ullage tank 104, the example fuel tank assembly 103 complies ormeets certain government regulations (e.g., regulations of the UnitedStates Coast Guard, Department of Transportation) that require allfittings coupled to a fuel tank to be located at a top wall or surfaceof a fuel tank.

Additionally or alternatively, in the illustrated example of FIG. 1, thebottom surface 114 of the ullage tank 104 is structured or configured todirect a fluid (e.g., liquid fuel) toward the opening 140 of the secondend 132 of the fuel path 128. For example, the bottom surface 114 may beconfigured to direct liquid fuel to a specified area (e.g., a centralarea or location) of the cavity 122 of the ullage tank 104. To channel,funnel and/or otherwise direct the liquid fuel to the specified area,the bottom surface 114 of the cavity 122 shown in the illustratedexample has a tapered, canted, convex and/or inverted conical-likeshape. The opening 140 of second end 132 of the fluid path 128 of theillustrated example is positioned in the cavity 122 adjacent an apex 144of the inverted conical-like bottom surface 114. Thus, as the liquidfuel in the cavity 122 of the ullage tank 104 drains or flows into thecavity 126 of the fuel tank 106, the bottom surface 114 channels,funnels and/or otherwise directs the liquid fuel in the cavity 122 ofthe ullage tank 104 towards the opening 142 of the second end 132 of thefluid path 128. As a result, substantially all of the liquid fuel in thecavity 122 of the ullage tank 104 is directed to the opening 140 of thesecond end 132 as the liquid fuel drains from the ullage tank 104.

In the illustrated example, a second fluid path 146 fluidly couples thecavity 122 of the ullage tank 104 and the vapor collection apparatus 110(i.e., a carbon canister) to prevent at least one of a vapor or gas fromflowing from the fuel tank assembly 103 into the atmosphere via the vent112. As shown in the example of FIG. 1, the second fluid path 146 iscoupled to the upper wall 136 of the ullage tank 104 via, for example, afitting 148. In other examples, the second fluid path 146 may be coupledto the vent 112 and the vapor collection apparatus 110 may be removed orbypassed.

In operation, the cavity 126 of the fuel tank 106 of the illustratedexample receives a fluid (e.g., liquid fuel) from a source (not shown)during a refilling process. When the cavity 126 of the fuel tank 106 isbeing filled, the volume or the level of liquid fuel within the cavity126 rises or increases. As the volume of the liquid fuel in the cavity126 increases, the fuel vapors and/or air within the cavity 126 arevented or displaced through the vent 112 via the cavity 122 of theullage tank 104 and the vapor collection apparatus 110 (e.g., a carboncanister). In this manner, fuel vapors entering the vapor collectionapparatus 110 pass through a filter material (e.g., carbon) in the vaporcollection apparatus 110 before passing to the vent 112. Emissions ofthe fuel vapors that are captured by the filter material and stored inthe vapor collection apparatus 110 are later returned or carried to thecavity 122 of the ullage tank 104 and/or the cavity 126 of the fuel tank106 when air is drawn from the vent 112 to fuel tank 106. For example,the stored emissions return to the fuel tank 106 as air is drawn fromthe atmosphere via the vent 112, through the vapor collection apparatus110, and to the cavity 126 of the fuel tank 106 via the first and secondfluid paths 128 and 146 and the cavity 122 of the ullage tank 104.

Also, as the cavity 126 of the fuel tank 106 of the illustrated exampleis being filled with the liquid fuel, the pressure within the cavity 126of fuel tank 106 may increase. As a result of a pressure increase in thecavity 126 of the fuel tank 106, the liquid fuel in the cavity 126 isdirected into the cavity 122 of the ullage tank 104 via the fluid path128 because the pressure in the cavity 122 of the ullage tank 104 issubstantially less than the pressure in the cavity 126 of the fuel tank106 during the filling event. Additionally or alternatively, at timesduring operation and/or non-operation of the marine craft 102, anincrease in temperature (e.g., due to a diurnal cycle) may cause theliquid fuel in the cavity 126 of the fuel tank 106 to expand. Thisincrease in pressure within the cavity 126 of the fuel tank 106 maycause the liquid fuel to expand and travel into the cavity 122 of theullage tank 104 via the fuel path 128.

As the excess liquid fuel enters the cavity 122 of the ullage tank 104of the illustrated example, the liquid fuel collects at the bottomsurface 114 of the cavity 122. Because the second end 132 of the fluidpath 128 is positioned adjacent the apex 144, the second end 132 becomessubmerged within the liquid fuel as the liquid fuel collects within thecavity 122 and rises toward the upper wall 136. As a result, the excessliquid fuel fills the cavity 122 of the ullage tank 104. Eventually, thepressure within the cavity 126 of the fuel tank 106 may decrease. Forexample, the pressure within the cavity 126 of the fuel tank 106 maydecrease as the filling event terminates and/or the temperature withinthe cavity 126 decreases (e.g., due to the diurnal cycle). Further, thecavity 122 of the ullage tank 104 of the illustrated example issubstantially at atmospheric pressure because the cavity 122 is fluidlycoupled to the vent 112. As a result, the pressures in the respectivecavities 122 and 126 of the ullage tank 104 and fuel tank 106substantially equalize (e.g., after a fueling event) when the liquidfuel is stored in the cavity 122 of the ullage tank 104. Further, due tothe elevation difference between the ullage tank 104 and the fuel tank106, the liquid fuel stored in the cavity 122 of the ullage tank 102 ofthe illustrated example provides a hydrostatic pressure or pressurehead. As described in greater detail below, hydrostatic pressure orpressure head provided by the liquid fuel in ullage tank 104 enables asiphon effect that may be initiated when the first end 130 of the fluidpath 128 is primed to start a liquid flow.

For example, a siphon effect of the illustrated example may be initiatedwhen a pressure within the cavity 126 of the fuel tank 106 decreases toa pressure that is less than a pressure of the cavity 122 of the ullagetank 104. For example, a siphon effect may be initiated during operationof the marine craft 102 as the engine 107 draws or demands the liquidfuel from the cavity 126 of the fuel tank 106 via the fuel line 108. Inparticular, the engine 107 creates a vacuum or suction at the first end130 of the fluid path 128 to draw the liquid fuel from the cavity 126 ofthe fuel tank 106, thereby causing the pressure in the cavity 126 todecrease. This vacuum or decrease in pressure in the cavity 126 of thefuel tank 106 can prime or initiate the siphon effect of the fuel tankassembly 103 to cause the liquid fuel in the cavity 122 of the ullagetank 104 to flow into the cavity 126 of the fuel tank 106 when thepressure in the fuel tank 106 is less than the pressure in the ullagetank 104. In the illustrated example, the liquid fuel flows from thecavity 122 of the ullage tank 104 and into the cavity 126 of the fueltank 106 when the siphon effect is primed because the elevation of theullage tank 104 relative to the fuel tank 106 provides a hydrostaticpressure that acts on the liquid fuel in the ullage tank 104. In otherwords, because a length 150 of a first portion 152 of the fuel path 128located between a third portion 154 of the fuel path 128 and the firstend 130 is greater than a length 156 of a second portion 158 of the fuelpath 128 located between the third portion 154 and the second end 132,the liquid fuel in the ullage tank 104 is able to flow into the cavity126 of the fuel tank 106 after the siphon effect is primed or initiated.The siphon effect allows or causes the liquid fuel in the ullage tank104 to be drawn back into the cavity 126 of the fuel tank 106 via thefluid path 128. Further, in the illustrated example, the second end 132of the fluid path 128 is submerged in the liquid fuel and is positionedadjacent the apex 144 of the bottom portion 114 of the cavity 122 toallow substantially all of the liquid fuel within the cavity 122 of theullage tank 104 to be drawn to the cavity 126 of the fuel tank 106 viathe siphon effect. As a result, substantially all of the liquid fuel inthe ullage tank 104 is able to return to the fuel tank 106 without theuse of, for example, a pump.

As noted above, the fuel tank assembly 103 of the illustrated example isself-draining because substantially all of the liquid fuel within thecavity 122 of the ullage tank 104 may empty into the cavity 126 of thefuel tank 106 without the use of an external mechanical force or device.Further, because the fittings 138 and 148 of the example fuel tankassembly 103 are coupled to the upper wall 136 of the ullage tank 104,the need to implement and/or position a drain or fitting on a side orbottom wall of the ullage tank 104 is eliminated. In turn, the examplefuel tank assembly 103 complies or meets certain government regulations(e.g., regulations of the United States Coast Guard, Department ofTransportation) requiring all fittings coupled to a fuel tank to belocated at a top wall of the fuel tank.

FIG. 2 is a flowchart of an example method 200 that may be used toassemble an example self-draining ullage fuel tank system disclosedherein such as the example fuel tank assembly 103 of FIG. 1. While theexample method 200 may be used to assemble an example fuel systemherein, one or more of the blocks and/or processes illustrated in FIG. 2may be combined, divided, re-arranged, omitted, eliminated and/orimplemented in any other way. Further still, the example method of FIG.2 may include one or more blocks in addition to, or instead of, thoseillustrated in FIG. 2, and/or may include more than one of any or all ofthe illustrated blocks. Although the example method 200 is describedwith reference to the flowchart illustrated in FIG. 2, many othermethods of assembling an example fuel tank system may alternatively beused. Because the example method 200 may be used to assemble the examplefuel tank system of FIG. 1, those components identified in FIG. 1 thathave functions substantially similar or identical to the functions ofthose components described below will not be described in detail again.Instead, the interested reader is referred to the above correspondingdescriptions. To facilitate this process, the same reference numberswill be used for like structures.

The example method to assemble an example self-draining ullage fuel tanksystem disclosed herein is discussed in connection with the example fueltank system 100 of FIG. 1. The example method 200 disclosed herein maybegin by providing a ullage tank 104 and a fuel tank 106 (block 202).For example, the ullage and fuel tanks 104 and 106 may be positionedwithin a boat and/or marine craft 102. Additionally or alternatively,the ullage tank 104 is positioned at a distance, elevation or height 116relative to the fuel tank 106 (block 204). For example, a bottom surface114 of the ullage tank 104 may be positioned near (e.g., above, alignedwith and/or slightly below) an upper wall 118 of the fuel tank 106spaced by the height 116.

Further, the ullage and fuel tanks 104 and 106 are fluidly coupled via afluid path 128 (block 206). For example, a first end 130 of the fluidpath 128 is coupled to the fuel tank 106 (block 208). In some instances,the first end 130 of the fluid path 128 is coupled to the fuel tank 106via a fitting, plastic welding, etc. In the example method 200, a secondend 132 of the fluid path 128 is at least partially positioned in acavity 122 of the ullage tank 104 via an opening 134 in an upper wall136 of the ullage tank 104 (block 210). In some instances, the secondend 132 is positioned adjacent a bottom portion 114 of the cavity 122 ofthe ullage tank 104. In some such instances, a support 142 may beprovided adjacent the bottom surface 114 to support or hold the secondend 132 of the fluid path 128 inside the cavity 122. Additionally oralternatively, in some instances, the bottom surface 114 may beconfigured with a tapered shape, a convex shape, an invertedconical-like shape and/or any other shape to channel or direct fluidtoward the opening 140 of the second end 132 of the fluid path 128. Insome such instances, the second end 122 of the fluid path 128 may bepositioned adjacent an apex 126 of the bottom portion 114.

Additionally or alternatively, the cavity 122 of the ullage tank 104 ofthe illustrated example may be fluidly coupled to a vent 112. In someinstances, a vapor collection apparatus 110 may be coupled between thevent 112 and the cavity 122 of the ullage tank 104 via a second fluidpath 146. In such instances, the second fluid path 146 is coupled to afitting 148 that is coupled to the upper wall 136 of the ullage tank104.

Although certain example methods, apparatus and articles of manufacturehave been described herein, the scope of coverage of this patent is notlimited thereto. On the contrary, this patent covers all methods,apparatus and articles of manufacture fairly falling within the scope ofthe appended claims either literally or under the doctrine ofequivalents.

What is claimed is:
 1. A fuel tank apparatus, comprising: a fuel tank; aullage tank positioned at an elevation relative to the fuel tank; and afluid path to fluidly couple a cavity of the fuel tank and a cavity ofthe ullage tank, the fluid path having a first end coupled to the cavityof the fuel tank, the fluid path having a second end extending throughan opening of an upper wall of the ullage tank and having an openingpositioned adjacent a bottom surface of the cavity of the ullage tank.2. The fuel tank apparatus of claim 1, wherein the fluid path is toprovide a siphon effect that is initiated when the first end of thefluid path is primed to start liquid flow.
 3. The fuel tank apparatus ofclaim 2, wherein the siphon effect is to draw fuel from the cavity ofthe ullage tank toward the cavity of the fuel tank.
 4. The fuel tankapparatus of claim 1, wherein the bottom surface of the cavity of theullage tank has a convex shape.
 5. The fuel tank apparatus of claim 1,wherein the opening is positioned adjacent an apex of the bottom surfaceof the cavity of the ullage tank.
 6. The fuel tank apparatus of claim 1,further comprising a second fluid path to fluidly couple the cavity ofthe ullage tank and a vent, the second fluid path being coupled to theupper wall of the ullage tank.
 7. An apparatus, comprising: a ullagetank defining a cavity to contain excess fuel from a cavity of a fueltank; and a fluid path to fluidly couple the cavity of the ullage tankand the cavity of the fuel tank, the fluid path positioned through anupper wall of the ullage tank, at least a portion of the fluid pathpositioned adjacent a bottom wall in the cavity of the ullage tank, thebottom wall being opposite the upper wall.
 8. The apparatus of claim 7,wherein the cavity of the ullage tank is positioned at an elevationrelative to the fuel tank.
 9. The apparatus of claim 8, wherein a firstend of the fluid path is primed to start liquid flow via a vacuum todraw excess fuel from the cavity of the ullage tank to the cavity of thefuel tank, the first end of the fluid path being coupled to the fueltank.
 10. The apparatus of claim 7, wherein the bottom wall of theullage tank has an inverted conical-like shape.
 11. The apparatus ofclaim 10, wherein a second end of the fluid path has an openingpositioned in the cavity adjacent an apex of the conical-like shape. 12.The apparatus of claim 7, further comprising a second fluid path coupledto the upper wall of the ullage tank, the second fluid path to fluidlycouple the cavity of the ullage tank and the atmosphere.
 13. A fuel tankapparatus, comprising: first means for containing fluid; second meansfor containing fluid positioned at an elevation relative to the firstmeans for containing fluid, the second means for containing fluid beingfluidly coupled to and configured to receive fuel from the first meansfor containing fluid; and means for fluidly coupling the first andsecond means for containing fluid, the means for fluidly couplingpassing through an opening in an upper wall of the second means forcontaining fluid and having a portion extending into a cavity of thesecond means for containing fluid and positioned adjacent a bottomportion of the second means for containing fluid.
 14. The apparatus ofclaim 13, further comprising means for supporting the portion of themeans for fluidly coupling extending into the cavity of the second meansfor fluidly coupling.
 15. The apparatus of claim 14, further comprisingmeans for attaching the portion of the means for fluidly coupling thatextends into the cavity to an upper wall of the second means for fluidlycoupling.
 16. The apparatus of claim 13, further comprising means forventing, the means for venting to fluidly couple the cavity of thesecond means for fluidly coupling and the atmosphere.
 17. A method forcoupling a fuel tank assembly, comprising: providing a fuel tank;providing a ullage tank; positioning the ullage tank at a heightrelative to the fuel tank; and fluidly coupling a cavity defined by thefuel tank and a cavity defined by the ullage tank via a fluid path, afirst end of the fluid path being coupled to the fuel tank, a second endof the fluid path being positioned through an upper wall of the ullagetank and at least partially positioned in the cavity of the ullage tank.18. The method of claim 17, wherein positioning the fluid path at leastpartially in the cavity of the ullage tank comprises positioning thesecond end of the fluid path adjacent a bottom portion of the ullagetank.
 19. The method of claim 18, further comprising fluidly couplingthe cavity of the ullage tank and the atmosphere via a vent.
 20. Themethod of claim 18, further comprising securing the second end of thefluid path adjacent the bottom portion of the ullage tank via acoupling.